Analytical Sciences

Aromatic versus Aliphatic α-Diimine Ligands in Heteroleptic Copper(I) Emitters: Photophysical and Electrochemical Properties

Masaki YOSHIDA, Sae YANAGIDA, Daisuke SAITO, Atsushi KOBAYASHI, and Masako KATO

Department of Chemistry, Faculty of Science, Hokkaido University, North-10 West-8, Kita, Sapporo, Hokkaido 060-0810, Japan

The electrochemical and photophysical properties of a heteroleptic Cu(I) complex bearing an aliphatic α-diimine ligand, [Cu(dab)(xantphos)]⁺ (Cu-dab; dab = N,N′-diphenyl-2,3-dimethyl-1,4-diazabutadiene, xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene), were evaluated together with those of complexes [Cu(dmp)(xantphos)]⁺ (Cu-dmp; dmp = 2,9-dimethyl-1,10-phenanthroline), [Cu(dmbpy)(xantphos)]⁺ (Cu-dmbpy; dmbpy = 5,5′-dimethyl-2,2′-bipyridine), and [Cu(bq)(xantphos)]⁺ (Cu-bq; bq = 2,2′-biquinoline), bearing aromatic diimine ligands. Cu-dab exhibited a two-step ligand-centered redox behavior, where the first wave corresponded to an electrochemically reversible one-electron reduction process. Although Cu(I)-aromatic diimine complexes Cu-dmp, Cu-dmbpy, and Cu-bq exhibited obvious luminescence from the metal-to-ligand charge transfer (MLCT) excited state, Cu-dab did not show any luminescence. Computational studies indicated that this non-luminescent property was caused by the large structural relaxation of Cu-dab during photoexcitation.

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